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Florida Energy Code Revision Highlights Cost-Effectiveness of Reflective Insulation for Masonry Walls

Posted by Paul Nutcher on November 07, 2013
Florida Energy Code Revision Highlights Cost-Effectiveness of Reflective Insulation for Masonry Walls
Masonry wall insulation installation. (Fi-Foil)

Buried in 2012 technical committee reports to the Florida Building Commission are new findings that show the cost per square foot is much less for energy code compliance in Florida with reflective insulation. Because of the technical studies and experts testimony, the 2013 Florida Building Code Energy Conservation sections will be rewritten with this new knowledge about the benefits of reflective insulation.

Furthermore, the experts found that the return on investment (ROI) for insulating a home or building can be less than improvements in building occupant behavior. For example, turning off lights when rooms are unoccupied can provide a higher ROI than adding foam board to the building envelope.

Going into the hearings, there was a perception that more insulation in masonry walls was a better choice than all of the other energy efficiency options. One cause for the perception is because walls make up a large portion of a building, therefore it would appear that the more insulation in the walls the more energy conservation possible for the building. While small increases in R-Values can be accomplished, there is a point of diminished return on R-Value for savings on energy loads such as heating and cooling, especially when taking into consideration the thermal mass of a concrete block home. Some experts argue that the benefits of thermal mass are not well represented in the current Florida Energy Code.

Energy Consumption Realities

In one report, the Building Commission heard that between the 2004 Florida Energy Code and the adoption in 2009 of a more stringent energy code, the actual savings in energy was much less for HVAC  heating and cooling while plug loads—such as coffee makers and electronic device chargers—actually consumed more energy. This conclusion was made possible with the Florida Solar Energy Centers energy calculation tool, EnergyGuage.

It turns out that occupants’ behavior in regards to plug loads would potentially result in greater energy savings than trying to further insulate the building envelope, especially with higher cost insulation solutions that were available on the market. The cost per R-value significantly impacts the results.

Initially, the Building Commission was going to propose increasing R-Values in masonry wall construction above IECC 2012 levels but this changed as experts were able to demonstrate that there is an appropriate amount of insulation for masonry walls that is needed due to masonry walls' thermal mass effects.

The committee had been considering changes to the 2013 Florida Energy Conservation Code to masonry walls (or mass walls) to go from R-3/4 to R-6/7.8 in Miami or Climate Zone 1; and go from R-6/6 to R-6/7.8 in Orlando and Tallahassee or Climate Zone 2. (Note: the numbers R-6 / 7.8 represent the amount of insulation required on the exterior or interior of the mass wall, respectively to meet the Prescriptive Code.)

The current IECC requires walls to be insulated to an R-Value of 4 unless the walls contain more than half of the total structure’s insulation. If that's the case, the walls must be insulated to an R-Value of 6. The current prescriptive R-Value requirement in the Florida energy code for mass walls is an R-Value of 6.

Furthermore, Principal Engineer Martha G. VanGeem, PE, LEED AP, FACI, explained to the committee that the thermal mass of masonry walls helps delay the transfer of heat through the walls of a structure regardless of the wall insulation, and especially in Climate Zone 1 (Miami) and Climate Zone 2 (Orlando and Tallahassee) will provide energy conserving benefits. VanGeem noted that the IECC accounts for this delay in thermal mass warming while FSEC’s EnergyGauge does not, and therefore can potentially underestimate the thermal mass effects on energy usage calculations. 

Lastly, DOE and other authorities have tentatively proposed code changes to the residential portion of the next version of the IECC due to be published in 2015 and those bodies “have not proposed any changes to the mass wall criteria in Climate Zones 1 and 2,” VanGeem testified. “This demonstrates that changes to increase the R-Values of mass walls in Florida above the current 2012 IECC levels are not warranted,” VanGeem added.

Cost Effectiveness of Reflective Insulation

The committee also examined cost increases for additional insulation of masonry walls and found that the installed cost per square foot to go to an R-Value of 7.1 with reflective insulation was 42 cents per square foot versus a foam product with a resulting R-Value of 7.8 would cost 67 cent per square foot. Furthermore, to meet the IECC prescriptive requirement of R-Value of 4, the equivalent R-Value with reflective insulation was just 16 cents per square foot.

With the above values, Jeff Sonne at FSEC found that builders would pay more than $700 more to construct a one-story 1,252-square-foot home with foam board than with reflective insulation to an R-Value of 7.1 and up to $900 more per 1788-square-foot two-story masonry wall home with foam board versus reflective insulation.

Further information was provided to the committee by VanGeem that showed the energy cost savings in going from an R-Value of 4 to R-Value of 7.8 was around $27 per year. The upfront cost of the additional insulation is roughly $1,300, not including the cost to the builder for modifications to the wall for increasing the thickness of the wall cavity by ¾ inch to take additional insulation. These costs consider not just the price of the insulation products from a distributor or store but also consider the labor and contractor’s profit, which is consistent with the establishment of a building’s baseline energy budget per ASHRAE 90.1 and 90.2 standards.

Don Beers of the Masonry Association of Florida explained, "'More is better' so it would seem that the more insulation you used the more energy efficient a building would become, yet the point of diminishing returns quickly reduces the efficiency of added wall insulation.”

Due to all the expert testimony, the Florida Building Commission determined that the IECC levels for R-Values in mass walls were to be adopted for the 2013 Florida Energy Code.

 

Paul Nutcher, CSI CDT, is president of Green Apple Group LLC.

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